1. Field of the Invention
This invention relates to photopolymerizable compositions and, more particularly, to a photopolymerizable composition comprising an unsaturated monomer, a photopolymerization initiator, and, if necessary, a linear organic high molecular weight polymer and a sensitizer. In particular, the invention relates to photopolymerizable compositions useful for photosensitive layers of photosensitive printing plates, photoresists, etc.
2. Description of the Prior Art
A method of making image reproductions by photographic means using a photosensitive composition composed of a mixture of a polymerizable ethylenically unsaturated compound, a photopolymerization initiator, and, if necessary, a soluble polymer having film-forming ability, a thermal polymerization preventing agent, etc., is presently widely known. U.S. Pat. Nos. 2,927,022, and 2,902,356 disclose that a photosensitive composition of this type has the ability to be hardened and insolubilized by irradiation with light and hence hardened images of the photopolymerizable composition can be formed by providing a film or layer of the photopolymerizable composition, exposing the film or layer through a negative of the desired image to light, and then removing unexposed portions with a suitable solvent. As a matter of course, the photopolymerizable composition of this type is very useful for making printing plates or resists.
However, because a polymerizable ethylenically unsaturated compound is not sufficiently sensitive, photopolymerization initiators such as benzil, benzoin, benzoin ethyl ether, Michler's ketone, anthraquinone, acridine, phenazine, benzophenone, 2-ethylanthraquinone, etc., have been added to the compound to increase sensitivity. However, using these photopolymerization initiators, a long exposure time is required for hardening due to the low response of the photopolymerizable compositions. This causes problems such as in case of reproducing precise images if the operation is disturbed even slightly by vibrations and images having good quality are not reproduced; the energy irradiation amount--intensity of the light source for exposure must be increased and hence it is necessary to release large amounts of generated heat, and further the films or layers of the composition are liable to be deformed and/or denatured by the heat.